The present invention relates to a device for fastening in a bone, preferably the cranial bone. Alternatively, the device may also be used in connection with tubular bones. The device is intended for use by momentary or continual supervision and examination of physical conditions in the inner cavities of the bone or behind the bone. Pathological conditions may be examined, as for example cerebral haemorrhage, oedema. squeezing off. extension of the ventricular system. dislocation of anatomical structures. tumours, accumulations of blood and liquid.
The invention is developed for and will especially be explained in connection with examination of accumulation in the cranial cavity and especially the content of this which is located behind the cranial bone. But it also gives advantages by use in tubular bones in order to examine developments in the bone marrow in the inner of the bone.
The invention furthermore relates to a kit comprising such a device, and which is intended for use by continual supervision and examination of physical conditions in the inner cavity of the bone or behind the bone. preferably in the cranial cavity.
Furthermore. the invention relates to the use of the device by continual supervision and examination of physical conditions in the cranial cavity.
Devices which have been used for examining physical conditions in the cranial cavity are known. However, the known devices are disadvantageous as they give a signal which occurs with a delay in relation to the physical condition which it is desired to supervise. Furthermore, it is a signal which indicates a stationary condition in the cranial cavity.
The known devices may also be disadvantageous by requiring greater surgical interventions necessitating sterile conditions and full anaesthesia. They are thus not suited for use in a hospital department where patients lie for observation.
The known devices and systems will be designed as explained in the following.
There is known a device whereby the pressure in the cranial cavity is supervised. This device may be placed without using full anaesthesia. The device may be removed without having to move the patient to a surgical department.
If a person is desired to be observed in order to detect physical conditions in the cranial cavity, for example, as a consequence of blows to the head, or as a supervision of a condition occurring after a surgical intervention, or for supervising a condition of sickness. it has been known to insert a screw through the cranial bone. This screw is hollow and has a point which passes through the membrane of the brain so that an open connection is established between the inner of the membrane of the brain and a manometer which is connected with the outer end of the screw situated outside the cranial bone.
On the manometer it is possible to register surpressure in the cranial cavity which is an indication of different subsequent damages which may occur in the cranial cavity. In practice, it has shown that these devices do not imply a great risk of infection. The intervention itself and the locating of the device, thus takes place without using full anaesthesia. However, the known system has a limitation as only an appearing increase in the pressure is occurring. It is not possible to determine a cause, which, for example, may be accumulations of blood or liquid in the cranial cavity.
Furthermore, the system will be tied to another drawback, because one will get an indication via the increase of pressure after an accumulation of blood or liquid has been built up through a certain time. Thus, a delay occurs before signal is received, and the signal is only an expression of a subsequent reaction.
Previously, there have been tests with measuring flow of blood to and from the cranial cavity. Through changes in the pressure in the blood supply vessels, it is possible to get an indication of a pressure built-up in the cranial cavity. This method is also disadvantageous by a delayed indication of a condition which is under development. This system is thus connected with the same drawbacks as mentioned above as one just get an indication of the symptom, and this indication comes with a delay.
For many years, a Doppler-ultrasound directly through the cranium has been used for measuring the rate of flow of blood. Because of the characteristic of the cranial bone, the ultrasound will have difficulty in penetrating and the measurements can therefore only be made in the temple region where the cranial bone is thinnest and allows penetration of ultrasound. With this access, it is not possible to achieve creation of an image of a technically usable quality.
Also, scanners are known, so-called CT-scanners and MR-scanners. Such scanners are, however, very costly in use. Furthermore, these are not devices which are practical in use in connection with beds in hospital departments where patients are admitted for observation.
As an expression of the need that has existed. it may be mentioned that in USA in 1992, 20 inhabitants out of 100,000 died because of so-called cranial traumas. The total number of severe cranial traumas is estimated to be about 5 times as large. The need for a supervision may thus be estimated to be several hundred thousand a year in the Western world. In spite of this need, there has until now not been proposed devices or methods for continual supervision with a cerebral image forming technique which is competitive in relation to the known scannings.
Previously, there has been proposed an equipment using ultrasound scanning of physical conditions in the cranial cavity. This equipment and the use thereof are described in International patent application WO 87/03190. This equipment is intended for mounting over a hole in the cranial bone formed for this purpose and is placed in a way so that it fits tightly to the cranial bone. However, this equipment and the described method are unfavourable as they require craniotomi, i.e. removal of a larger piece of bone. The equipment has to be used under full anaesthesia and under sterile conditions and is intended for use in connection with neurosurgical interventions in the cranial cavity. Use of the described equipment will thus be very demanding on resources, because of requirements of sterile conditions and requirements of full anaesthesia. This is the case with locating as well as the subsequent supervision situation.
The equipment is furthermore unfavourable as a risk of contamination occurs. In the system, there is used a transducer which in principle participates in the closing of the formed hole in the cranial bone. As the equipment comprises elements making possible access of different instruments to the cranial cavity, we are speaking about a complete system which cannot be said to be closed, and thereby a system which may be considered to be used under unsterile conditions.
The equipment furthermore requires complicated fastening in the opening formed in the cranial bone by means of a clamping technique. Even though the described equipment makes possible the creation of an image of physical conditions in the cranial cavity, it will not be suitable for use for continual supervision and examination of the cranial cavity on persons situated in unsterile hospital departments.
A holder that may be fastened in a bone, for example the cranium, is known from U.S. Pat. No. 4,681,103. This holder may be used for an ultrasound transducer. This holder is, however, open towards the inner of the cranium and may thus not be used outside a sterile area in a hospital. This holder and the equipment belonging to it in the form of an ultrasound transducer and a needle on the described apparatus, may thus not be used for supervision, but only to perform localisation of a spot by means of an ultrasound transducer in connection with a surgical intervention. After determining the positioning, a guide is adjusted in the holder. Subsequently, this guide is used as support for the needle. There is no precise indication of how to ensure a correct screwing of the holder into the bone.
From American U.S. Pat. No. 5,054,497 there is known an equipment which may be fastened in a bone, for example the cranial bone. In this equipment, there is no description of a possibility of supervision. The equipment is used in connection with the previously mentioned pressure measurement which is disadvantageous by giving a delayed indication of conditions in the brain. The described system will contain openings which do not make it usable in hospital sections outside sterile areas. The system is thus only usable for use in connection with operations and not for use by continual supervisions.
Thus, there exists a need for a technique making possible creation of an image for physical conditions in the cranial cavity. In order to achieve the best utility, there will especially be a need for an image forming technique making possible a three-dimensional creation of an image by scanning, and especially a scanning which may be performed continually without need for sterile conditions, full anaesthesia, etc. during the supervision, as this is very demanding on resources and work. Thus, there is need for an image forming technique which makes possible a scanning which may be performed continually at the bed of the patient in a non-sterile department of a hospital, for example where patients are lying for observation.
It is the purpose of the present invention to indicate a device, a kit of which the device concern and a use of these elements by a method where there is performed a creation of an image of physical conditions in the inner of a bone or behind the bone and preferably in the cranial cavity through a brain scanning, which takes place by use of a signal transducer which outside a sterile area makes possible a continual supervision of the physical condition, which for example may be a blood or a liquid accumulation in the cranial cavity.
According to the present invention this purpose is achieved with a device for fastening in a bone, preferably the cranial bone, for use by continual supervision and examination of physical conditions in the internal cavities of the bone or behind the bone, preferably in the cranial cavity, which device comprises a signal transducer and a guide having an internal hollow space for receiving the signal transducer comprising a signal transmitting and receiving means, preferably an ultrasound transducer in which the guide at the end facing the inner of the bone when using the device is covered by a signal penetrable membrane, and that the guide has engagement means for cooperating with corresponding engagement means on a tool which is used for clamping the guide into a previously drilled hole in the bone.
According to the present invention it is possible to provide the guide in the shape of a screw with a thread which may be brought into engagement with the previously drilled hole. Alternatively, the guide may be provided in the form of a hollow cylindrical plug, which in its cylindrical surface has a boring open to the outer side with a rotatably supported stud having an asymmetrical cross-section with projecting engagement means which by rotation of the stud engages the previously drilled hole.
According to the present invention, there is used a kit as described in the subsequent claims 8, 9 or 10.
According to the invention the above described device and kit for momentary or continuous supervision and examination of the development of blood or liquid accumulations in the cranial cavity, where the signal transducer is provided in the form of an ultrasound transducer, where the crystal is of a kind arranged for creating a three-dimensional image by processing the received/transmitted signals. This technique may, for example, be based on a three-dimensional pulse/echo image creating method where a wide band wave pulse is used for transmitting, and where rays with different parameters with limited diffraction are used for reception. In such a method, the received signals are processed via fourier-transformation whereby there is created three-dimensional images by a single transmission. Alternatively, application of the device may take place with a signal transducer where the crystal or transducer is rotated between different angular positions, and where the registered signals from each of the angular positions are collected and used for creating a three-dimensional image matrix of the accumulation.
After having bored a hole through the bone, the screw or plug forming a part of the device may be placed very simply and easily. Beside the bored hole, one may possibly provide a relieving hole for pressure equalisation of a possible surpressure which arises at the mounting of the screw. This relieving hole may possibly also be used for introducing liquid and improving the acoustical contact.
If the screw comprises a self-cutting thread there will be achieved an especially simple mounting as you just have to drill a hole with a suitable diameter whereafter the self-cutting thread establishes the thread and thereby the fastening of the screw in the bone. When the screw is located, there is no physical contact between the inner hollow space of the bone and the surrounding environment. There is thus little risk of infection.
It is possible to drill a hole with the same technique which earlier was used in connection with a pressure sensor. When the screw is placed in the bored hole in the cranial bone, this takes place in such a way the signal penetrable membrane is brought into contact with the outer brain membrane.
The screw is arranged very easily by means of the screwing tool which may be of any known kind. Thus, we may be speaking of a screw with a polygonal head which cooperate with a corresponding key. as well as there also may be spoken about a screw with an internal angular cross-section intended to cooperate with a screwing tool of the unbraco type which is placed inside the hollow space of the screw during the screwing.
If the screw and the transducer are made as separate units, the transducer is placed afterwards in the hollow space of the screw. If there is a need for this, the transducer may be applied a gel for achieving a better contact with the signal penetrable membrane. This gel may be placed on a transducer before it is placed in the hollow space of the screw or may be inserted via channels formed between the wall in the hollow space of the screw and the outer side of the transducer.
Between the screw and the transducer, there is provided means which ensure a mutual fixing. This means may be a thread, the bayonet socket click systems, abutting surface/collar or other systems known per se making possible the creation of mutual well-defined positions for those elements. When the crystal of the transducer or the transducer itself is rotated between different positions where there is formed two-dimensional images, it is possible to combine the signals from these positions and create a three-dimensional image matrix which gives a sure indication of the development of an accumulation. Furthermore, there may be performed Doppler-ultrasound of any modality.
The screw may be made of a tissue friendly material, as for example surgical steel. There may also be used plastic. as for example PEEK or POM. However, it is also possible to use other kinds of plastic or metal.
The signal penetrable membrane at the inwards facing end of the screw may be formed of polyester, polycarbonate, or Surlyn. Other materials may also be used. The membrane may have a thickness between about 0.2 mm and 0.8 mm, which gives a sufficiently good ultrasound penetrability.
The membrane is fastened to the screw by bonding, welding or another method of fastening known by itself. Alternatively, screws and membranes are moulded in one piece. In order to ensure the best possible conditions for signals with the purpose refracting and focusing of the signal ray and reduction of so-called side loops, the shape of the membrane is adapted for the transducer.
The membrane may comprise a flexible pad, for example of silicone, natriumchloride. or another signal penetrable material, in order to improve the acoustical contact between the screw and the outer brain membrane.
The tool has a polygonal profile for the purpose of fitting over a corresponding polygonal profile on the screw and has furthermore a fitting handle which makes possible operation with one hand. The tool has preferably a guiding stud fitting into the hollow space of the screw. Hereby the screw is guided during the screwing. If the guide stud has pins or grooves to cooperate with corresponding grooves or pins in the hollow space of the screw, there is achieved a distribution of the forces necessary for the screwing whereby the outer diameter of the screw may favourably be minimised.
In a practical design of the tool, the stud may be provided with 2-4 elongate pins extending over the whole length of the stud and which have a height of about 0.25 mm and a width of about 1 mm. The elongate pins cooperate with corresponding grooves formed in the hollow space of the screw. It is desired to reduce the outer diameter of the screw the most possible in relation to the inner diameter which is determined by the applied transducer.
The outer diameter of the screw is preferably under about 20 mm, preferably down to 12-14 mm. In practice, it has shown that holes in the cranial bone with dimensions under about 20 mm will be closed by themselves.
If the guide is formed as a cylindrical plug there will also be created a hole in the cranial bone with the same technique as described above. Also, plugs could be placed in the hole with the signal penetrable membrane in contact with the outermost brain membrane.
The plug is placed with a slight interference fit in the previously bored hole. The part of the boring in the cylinder wall of the plug open to the outside will be flush with the outside of the asymmetrical stud when this is turned to its inactive position. The stud at its outwards facing end is provided with a notch or a polygonal hole which cooperate with a screw driver, unbraco key, or the like. By rotating the stud, the projecting engagement means are brought out of the open part of the boring and thereby outside the external cylinder surface of the plug. The engagement means are thereby brought into engagement with the wall in the previously bored hole. The engagement means on such a stud may be shaped as threads or as projecting beads penetrating into the bone tissue and thereby clamps and holds the plug.
In the plug the membrane may be formed and fastened as described above in connection with the screw. Thus, it will also be possible to make plug and membrane by moulding in one piece.
The device according to the invention as mentioned above will primarily be used for continual supervision and preferably in neurosurgical departments where a xe2x80x9cwindowxe2x80x9d to the cranial cavity is created. The device is especially usable by supervision of the development in liquid or blood accumulations. In order to create a three-dimensional image, the transducer may take a picture, for example for every rotation of 5-10xc2x0 of the crystal. Hereafter an electronical processing of the formed two-dimensional images takes place in order to establish a three-dimensional image matrix which gives a clear overview of the development of a physical condition in the cranial cavity.
The image processing will usually be performed in a scanner, which is an expensive instrument. According to the invention it will be possible to let the devices form a part of a system which comprises one scanner that arbitrarily may be coupled together with different transducers. Thus, it will be possible with a centrally located scanner to perform a supervision of a larger number of patients who each are provided with a device according to the invention. The scanner may be operated according to a preselected cycle so that a cyclical supervision sequence of a number of patients is performed.
The invention may be used for patients having cranial traumas, for example, because of car accidents, shooting, falling and the like. The device may also be used for patients who have a spontaneous bleeding (aneurysm), for supervising the growth and risk of bursting of the blood vessels. The device may also be used on an operating table, for example by brain surgery where. for example, a tumour is removed. The device makes it possible to get a momentary and sure documentation that all of the tumour is removed. It will also be possible to use the device subsequently by supervising the patient in order to examine if any subsequent bleeding occurs. Oedema may also be localised by use of the device according to the invention. Likewise, it will also be possible to localise a hygroma. Because such hygromas may occur several times in succession, the device will be very suitable for a continuous supervision where a scanning/supervision is performed from time to time.
In practice, it will be possible to use several devices which are placed, for example, in the cranial bone. As the transducers will have a limited cover angle, it will be necessary in certain cases to use two or more transducers. The signals from the two transducers may be combined via software in order to create a single image of the whole cranial cavity.
Alternatively, it will also be possible to produce a transducer where the crystal inside the transducer is movable more than the previously mentioned rotation, thereby to achieve a greater cover angle for the transducer. Today there are commercially available transducers which are so small that transducers could be formed with diameters down to 6-10 mm. If a transducer of a diameter of up to 20 mm is used, where in practice it turns out that the hole may close by itself by forming of connective tissue, it will be possible to use a small crystal which is movable inside the transducer head in order to achieve a great cover angle.
When the device according to the invention is used, the crystal of the transducer will create an image which runs axially in the longitudinal direction of the transducer and the screw. The outwards facing end of the device will be situated outside the surface of the bone. The device may be provided with a point making possible a quick electrical coupling together of the transducer and a scanner. Alternatively, the device may be arranged in such a way that the transducer is detachably mounted in the guide. Hereby, one and the same transducer may be used for supervising several patients provided with a guide.